Carbon monoxide protects against ischemia-reperfusion injury in an experimental model of controlled nonheartbeating donor kidney

Metal-based carbon monoxide releasing molecules with promising cytotoxic properties

Carbon monoxide, the "silent killer" gas, is increasingly recognised as an important signalling molecule in human physiology, which has beneficial biological properties. A particular way of achieving controlled CO administration is based on the use of biocompatible molecules that only release CO when triggered by internal or external factors. These approaches include the development of pharmacologically effective prodrugs known as CO releasing molecules (CORMs), which can supply biological systems with CO in well-regulated doses. An overview of transition metal-based CORMs with cytotoxic properties is here reported. The mechanisms at the basis of the biological activities of these molecules and their potential therapeutical applications with respect to their stability and CO releasing properties have been discussed. The activation of metal-based CORMs is determined by the type of metal and by the nature and features of the auxiliary ligands, which affect the metal core electronic density and therefore the prodrug resistance towards oxidation and CO release ability. A major role in regulating the cytotoxic properties of these CORMs is played by CO and/or CO-depleted species. However, several mysteries concerning the cytotoxicity of CORMs remain as intriguing questions for scientists.

Pushing the boundaries of innovation: the potential of ex vivo organ perfusion from an interdisciplinary point of view

Ex vivo machine perfusion (EVMP) is an emerging technique for preserving explanted solid organs with primary application in allogeneic organ transplantation. EVMP has been established as an alternative to the standard of care static-cold preservation, allowing for prolonged preservation and real-time monitoring of organ quality while reducing/preventing ischemia-reperfusion injury. Moreover, it has paved the way to involve expanded criteria donors, e.g., after circulatory death, thus expanding the donor organ pool. Ongoing improvements in EVMP protocols, especially expanding the duration of preservation, paved the way for its broader application, in particular for reconditioning and modification of diseased organs and tumor and infection therapies and regenerative approaches. Moreover, implementing EVMP for in vivo-like preclinical studies improving disease modeling raises significant interest, while providing an ideal interface for bioengineering and genetic manipulation. These approaches can be applied not only in an allogeneic and xenogeneic transplant setting but also in an autologous setting, where patients can be on temporary organ support while the diseased organs are treated ex vivo, followed by reimplantation of the cured organ. This review provides a comprehensive overview of the differences and similarities in abdominal (kidney and liver) and thoracic (lung and heart) EVMP, focusing on the organ-specific components and preservation techniques, specifically on the composition of perfusion solutions and their supplements and perfusion temperatures and flow conditions. Novel treatment opportunities beyond organ transplantation and limitations of abdominal and thoracic EVMP are delineated to identify complementary interdisciplinary approaches for the application and development of this technique.

How to Best Protect Kidneys for Transplantation-Mechanistic Target

The increasing number of patients on the kidney transplant waiting list underlines the need to expand the donor pool and improve kidney graft utilization. By protecting kidney grafts adequately from the initial ischemic and subsequent reperfusion injury occurring during transplantation, both the number and quality of kidney grafts could be improved. The last few years have seen the emergence of many new technologies to abrogate ischemia-reperfusion (I/R) injury, including dynamic organ preservation through machine perfusion and organ reconditioning therapies. Although machine perfusion is gradually making the transition to clinical practice, reconditioning therapies have not yet progressed from the experimental setting, pointing towards a translational gap. In this review, we discuss the current knowledge on the biological processes implicated in I/R injury and explore the strategies and interventions that are being proposed to either prevent I/R injury, treat its deleterious consequences, or support the reparative response of the kidney. Prospects to improve the clinical translation of these therapies are discussed with a particular focus on the need to address multiple aspects of I/R injury to achieve robust and long-lasting protective effects on the kidney graft.

Strategies toward Metal-Free Carbon Monoxide Prodrugs: An Update

Carbon monoxide is an important gasotransmitter in mammals, with pleiotropic therapeutic potential against a wide range of human diseases. However, clinical translation of CO is severely hampered by the lack of a reliable CO delivery form. The development of metal-free CO prodrugs is the key to resolving such delivery issues. Over the past three years, some new exciting progress has been made in this field. In this review, we highlight these advances and discuss related issues.

Water-Soluble Carbon Monoxide-Releasing Molecules (CORMs)

Carbon monoxide-releasing molecules (CORMs) are promising candidates for producing carbon monoxide in the mammalian body for therapeutic purposes. At higher concentrations, CO has a harmful effect on the mammalian organism. However, lower doses at a controlled rate can provide cellular signaling for mandatory pharmacokinetic and pathological activities. To date, exploring the therapeutic implications of CO dose as a prodrug has attracted much attention due to its therapeutic significance. There are two different methods of CO insertion, i.e., indirect and direct exogenous insertion. Indirect exogenous insertion of CO suggests an advantage of reduced toxicity over direct exogenous insertion. For indirect exogenous insertion, researchers are facing the issue of tissue selectivity. To solve this issue, developers have considered the newly produced CORMs. Herein, metal carbonyl complexes (MCCs) are covalently linked with CO molecules to produce different CORMs such as CORM-1, CORM-2, and CORM-3, etc. All these CORMs required exogenous CO insertion to achieve the therapeutic targets at the optimized rate under peculiar conditions or/and triggering. Meanwhile, the metal residue was generated from i-CORMs, which can propagate toxicity. Herein, we explain CO administration, water-soluble CORMs, tissue accumulation, and cytotoxicity of depleted CORMs and the kinetic profile of CO release.

Luminal Administration of a Water-soluble Carbon Monoxide-releasing Molecule (CORM-3) Mitigates Ischemia/Reperfusion Injury in Rats Following Intestinal Transplantation

BACKGROUND

The protective effects of carbon monoxide (CO) against ischemia/reperfusion (IR) injury during organ transplantation have been extensively investigated. Likewise, CO-releasing molecules (CORMs) are known to exert a variety of pharmacological activities via liberation of controlled amounts of CO in organs. Therefore, we hypothesized that intraluminal administration of water-soluble CORM-3 during cold storage of intestinal grafts would provide protective effects against IR injury.

METHODS

Orthotopic syngeneic intestinal transplantation was performed in Lewis rats following 6 h of cold preservation in Ringer solution or University of Wisconsin solution. Saline containing CORM-3 (100 µmol/L) or its inactive counterpart (iCORM-3) was intraluminally introduced in the intestinal graft before cold preservation.

RESULTS

Histopathological analysis of untreated and iCORM-3-treated grafts revealed a similar erosion and blunting of the intestinal villi. These changes in the mucosa structure were significantly attenuated by intraluminal administration of CORM-3. Intestinal mucosa damage caused by IR injury led to considerable deterioration of gut barrier function 3 h postreperfusion. CORM-3 significantly inhibited upregulation of proinflammatory mRNA levels, ameliorated intestinal morphological changes, and improved graft blood flow and mucosal barrier function. Additionally, CORM-3-treated grafts increased recipient survival rates. Pharmacological blockade of soluble guanylyl cyclase activity significantly reversed the protective effects conferred by CORM-3, indicating that CO partially mediates its therapeutic actions via soluble guanylyl cyclase activation.

CONCLUSIONS

Our study demonstrates that luminally delivered CORM-3 provides beneficial effects in cold-stored rat small intestinal grafts and could be an attractive therapeutic application of CO in the clinical setting of organ preservation and transplantation.

Carbon monoxide mechanism of protection against renal ischemia and reperfusion injury

Carbon monoxide is quickly moving past its historic label as a molecule once feared, to a therapeutic drug that modulates inflammation. The development of carbon monoxide releasing molecules and utilization of heme oxygenase-1 inducers have shown carbon monoxide to be a promising therapy in reducing renal ischemia and reperfusion injury and other inflammatory diseases. In this review, we will discuss the developments and application of carbon monoxide releasing molecules in renal ischemia and reperfusion injury, and transplantation. We will review the anti-inflammatory mechanisms of carbon monoxide in respect to mitigating apoptosis, suppressing dendritic cell maturation and signalling, inhibiting toll-like receptor activation, promoting anti-inflammatory responses, and the effects on renal vasculature.

Perfusate Composition and Duration of Ex-Vivo Normothermic Perfusion in Kidney Transplantation: A Systematic Review

Ex-vivo normothermic perfusion (EVNP) is an emerging strategy in kidney preservation that enables resuscitation and viability assessment under pseudo-physiological conditions prior to transplantation. The optimal perfusate composition and duration, however, remain undefined. A systematic literature search (Embase; Medline; Scopus; and BIOSIS Previews) was conducted. We identified 1,811 unique articles dating from January 1956 to July 2021, from which 24 studies were deemed eligible for qualitative analysis. The perfusate commonly used in clinical practice consisted of leukocyte-depleted, packed red blood cells suspended in Ringer’s lactate solution with Mannitol, dexamethasone, heparin, sodium bicarbonate and a specific nutrient solution supplemented with insulin, glucose, multivitamins and vasodilators. There is increasing support in preclinical studies for non-blood cell-based perfusates, including Steen solution, synthetic haem-based oxygen carriers and acellular perfusates with supraphysiological carbogen mixtures that support adequate oxygenation whilst also enabling gradual rewarming. Extended durations of perfusion (up to 24 h) were also feasible in animal models. Direct comparison between studies was not possible due to study heterogeneity. Current evidence demonstrates safety with the aforementioned widely used protocol, however, extracellular base solutions with adequate oxygenation, supplemented with nutrient and metabolic substrates, show promise by providing a suitable environment for prolonged preservation and resuscitation.

Systematic Review Registration:https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021231381, identifier PROSPERO 2021 CRD42021231381

Carbon Monoxide in Pancreatic Islet Transplantation: A New Therapeutic Alternative to Patients With Severe Type 1 Diabetes Mellitus

Pancreatic islet transplantation is a minimally invasive procedure to replace β-cells in a subset of patients with autoimmune type 1 diabetic mellitus, who are extremely sensitive to insulin and lack counter-regulatory measures, and thereby increasing their risk of neuroglycopenia and hypoglycemia unawareness. Thus, pancreatic islet transplantation restores normoglycemia and insulin independence, and prevents long-term surgical complications associated with whole-organ pancreas transplantation. Nonetheless, relative inefficiency of islet isolation and storage process as well as progressive loss of islet function after transplantation due to unvoidable islet inflammation and apoptosis, hinder a successful islet transplantation. Carbon monoxide (CO), a gas which was once feared for its toxicity and death at high concentrations, has recently emerged as a medical gas that seems to overcome the challenges in islet transplantation. This minireview discusses recent findings about CO in preclinical pancreatic islet transplantation and the underlying molecular mechanisms that ensure islet protection during isolation, islet culture, transplantation and post-transplant periods in type 1 diabetic transplant recipients. In addition, the review also discusses clinical translation of these promising experimental findings that serve to lay the foundation for CO in islet transplantation to replace the role of insulin therapy, and thus acting as a cure for type 1 diabetes mellitus and preventing long-term diabetic complications.

Application of carbon monoxide in kidney and heart transplantation: A novel pharmacological strategy for a broader use of suboptimal renal and cardiac grafts

Carbon monoxide (CO) was historically regarded solely as a poisonous gas that binds to hemoglobin and reduces oxygen-carrying capacity of blood at high concentrations. However, recent findings show that it is endogenously produced in mammalian cells as a by-product of heme degradation by heme oxygenase, and has received a significant attention as a medical gas that influences a myriad of physiological and pathological processes. At low physiological concentrations, CO exhibits several therapeutic properties including antioxidant, anti-inflammatory, anti-apoptotic, anti-fibrotic, anti-thrombotic, anti-proliferative and vasodilatory properties, making it a candidate molecule that could protect organs in various pathological conditions including cold ischemia-reperfusion injury (IRI) in kidney and heart transplantation. Cold IRI is a well-recognized and complicated cascade of interconnected pathological pathways that poses a significant barrier to successful outcomes after kidney and heart transplantation. A substantial body of preclinical evidence demonstrates that CO gas and CO-releasing molecules (CO-RMs) prevent cold IRI in renal and cardiac grafts through several molecular and cellular mechanisms. In this review, we discuss recent advances in research involving the use of CO as a novel pharmacological strategy to attenuate cold IRI in preclinical models of kidney and heart transplantation through its administration to the organ donor prior to organ procurement or delivery into organ preservation solution during cold storage and to the organ recipient during reperfusion and after transplantation. We also discuss the underlying molecular mechanisms of cyto- and organ protection by CO during transplantation, and suggest its clinical use in the near future to improve long-term transplantation outcomes.

Machine perfusion of donor organs for transplantation

The ever-widening gap between organ supply and demand has resulted in an organ shortage crisis that affects patients all over the world. For decades, static cold storage (SCS) was the gold standard preservation strategy because of its simplicity and cost-effectiveness, but the rising unmet demand for donor organ transplants has prompted investigation into preservation strategies that can expand the available donor pool. Through ex vivo functional assessment of the organ prior to transplant, newer methods to preserve organs such as perfusion-based therapy can potentially expand the available organ pool. This review will explain the physiologic rationale for SCS before exploring the advantages and disadvantages associated with the two broad classes of preservation strategies that have emerged to address the crisis: hypothermic and normothermic machine perfusion. A detailed analysis of how each preservation strategy works will be provided before investigating the current status of clinical data for each preservation strategy for the kidney, liver, pancreas, heart, and lung. For some organs there is robust data to support the use of machine perfusion technologies over SCS, and in others the data are less clear. Nonetheless, machine perfusion technologies represent an exciting frontier in organ preservation research and will remain a crucial component of closing the gap between organ supply and recipient demand.

Cell therapy during machine perfusion

There has been increasing use of organs from extended criteria or donation after circulatory death donors to meet the demands of the transplant waiting list. Over the past decade, there has been considerable progress in technologies to preserve organs prior to transplantation to improve the function of these marginal organs. This has led to the development of normothermic machine perfusion, whereby an organ is perfused with warmed, oxygenated blood and nutrients to resume normal physiological function in an isolated ex-vivo platform. With this advance in preservation comes significant opportunities to recondition, repair and regenerate organs prior to transplantation using cellular therapies. This review aims to discuss the possibilities of machine perfusion technology; highlighting the potential for organ-directed reconditioning and the future avenues for investigation in this field.

Carbon monoxide: An emerging therapy for acute kidney injury

Treating acute kidney injury (AKI) represents an important unmet medical need both in terms of the seriousness of this medical problem and the number of patients. There is also a large untapped market opportunity in treating AKI. Over the years, there has been much effort in search of therapeutics with minimal success. However, over the same time period, new understanding of the underlying pathobiology and molecular mechanisms of kidney injury have undoubtedly helped the search for new therapeutics. Along this line, carbon monoxide (CO) has emerged as a promising therapeutic agent because of its demonstrated cytoprotective, and immunomodulatory effects. CO has also been shown to sensitize cancer, but not normal cells, to chemotherapy. This is particularly important in treating cisplatin-induced AKI, a common clinical problem that develops in patients receiving cisplatin therapies for a number of different solid organ malignancies. This review will examine and make the case that CO be developed into a therapeutic agent against AKI.

Dissemination of a novel organ perfusion technique: ex vivo normothermic perfusion of deceased donor kidneys

Ex vivo normothermic perfusion (EVNP) technology is a promising means of organ preservation, assessment, and preconditioning prior to kidney transplantation, which has been pioneered by a single group. We describe the challenges of setting up clinical EVNP programs in 2 new centers, as well as early patient outcomes. Governance, training, and logistical pathways are described. In order to demonstrate safety and proficiency in this new technique, early patient outcomes are also described. Patient outcomes included the incidence of primary nonfunction, delayed graft function, graft and patient survival at 1 year. Contralateral kidneys undergoing static cold storage alone were used as a comparator group. Between March 2016 and July 2017, EVNP was performed on 14 kidneys from 12 donors (11 kidneys in center 1, 3 kidneys in center 2). Of the 14 kidneys that underwent EVNP, 12 organs were implanted into 10 recipients. Two pairs of kidneys were implanted as dual grafts and 1 kidney was implanted simultaneously with a pancreas. The remaining 7 kidneys were transplanted as single allografts. Seven pairs of kidneys were available for paired analysis comparing EVNP versus static cold storage. Graft and patient outcomes were comparable between the 2 preservation techniques. The introduction of a clinical EVNP service requires a careful multimodal approach, drawing on the expertise of specialists in transplantation, hematology, and microbiology. Both new clinical EVNP programs demonstrated proficiency and safety when a structured dissemination process was followed.

Targeting Heme Oxygenase-1 in Cardiovascular and Kidney Disease

Heme oxygenase (HO) plays an important role in the cardiovascular system. It is involved in many physiological and pathophysiological processes in all organs of the cardiovascular system. From the regulation of blood pressure and blood flow to the adaptive response to end-organ injury, HO plays a critical role in the ability of the cardiovascular system to respond and adapt to changes in homeostasis. There have been great advances in our understanding of the role of HO in the regulation of blood pressure and target organ injury in the last decade. Results from these studies demonstrate that targeting of the HO system could provide novel therapeutic opportunities for the treatment of several cardiovascular and renal diseases. The goal of this review is to highlight the important role of HO in the regulation of cardiovascular and renal function and protection from disease and to highlight areas in which targeting of the HO system needs to be translated to help benefit patient populations.

CO-Releasing Materials: An Emphasis on Therapeutic Implications, as Release and Subsequent Cytotoxicity Are the Part of Therapy

The CO-releasing materials (CORMats) are used as substances for producing CO molecules for therapeutic purposes. Carbon monoxide (CO) imparts toxic effects to biological organisms at higher concentration. If this characteristic is utilized in a controlled manner, it can act as a cell-signaling agent for important pathological and pharmacokinetic functions; hence offering many new applications and treatments. Recently, research on therapeutic applications using the CO treatment has gained much attention due to its nontoxic nature, and its injection into the human body using several conjugate systems. Mainly, there are two types of CO insertion techniques into the human body, i.e., direct and indirect CO insertion. Indirect CO insertion offers an advantage of avoiding toxicity as compared to direct CO insertion. For the indirect CO inhalation method, developers are facing certain problems, such as its inability to achieve the specific cellular targets and how to control the dosage of CO. To address these issues, researchers have adopted alternative strategies regarded as CO-releasing molecules (CORMs). CO is covalently attached with metal carbonyl complexes (MCCs), which generate various CORMs such as CORM-1, CORM-2, CORM-3, ALF492, CORM-A1 and ALF186. When these molecules are inserted into the human body, CO is released from these compounds at a controlled rate under certain conditions or/and triggers. Such reactions are helpful in achieving cellular level targets with a controlled release of the CO amount. However on the other hand, CORMs also produce a metal residue (termed as i-CORMs) upon degradation that can initiate harmful toxic activity inside the body. To improve the performance of the CO precursor with the restricted development of i-CORMs, several new CORMats have been developed such as micellization, peptide, vitamins, MOFs, polymerization, nanoparticles, protein, metallodendrimer, nanosheet and nanodiamond, etc. In this review article, we shall describe modern ways of CO administration; focusing primarily on exclusive features of CORM's tissue accumulations and their toxicities. This report also elaborates on the kinetic profile of the CO gas. The comprehension of developmental phases of CORMats shall be useful for exploring the ideal CO therapeutic drugs in the future of medical sciences.

Twenty-four-hour normothermic perfusion of discarded human kidneys with urine recirculation

Transportable normothermic kidney perfusion for 24 hours or longer could enable viability assessment of marginal grafts, increased organ use, and improved transplant logistics. Eleven clinically declined kidneys were perfused normothermically, with 6 being from donors after brain death (median cold ischemia time 33 ± 36.9 hours) and 5 being from donors after circulatory death (36.2 ± 38.3 hours). Three kidneys were perfused using Ringer's lactate to replace excreted urine volume, and 8 kidneys were perfused using urine recirculation to maintain perfusate volume without fluid replenishment. In all cases, normothermic perfusion either maintained or slightly improved the histopathologically assessed tubular condition, and there was effective urine production in kidneys from both donors after brain death and donors after circulatory death (2367 ± 1798 mL vs 744.4 ± 198.4 mL, respectively; P = .44). Biomarkers, neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1 were successfully detected and quantified in the perfusate. All kidneys with urine recirculation were readily perfused for 24 hours (n = 8) and exhibited physiological perfusate sodium levels (140.7 ± 1.2 mmol/L), while kidneys without urine recirculation (n = 3) achieved a reduced normothermic perfusion time of 7.7 ± 1.5 hours and significantly higher perfusate sodium levels (159.6 ± 4.63 mmol/:, P < .01). Normothermic machine perfusion of human kidneys for 24 hours appears to be feasible, and urine recirculation was found to facilitate the maintenance of perfusate volume and homeostasis.

The future of marginal kidney repair in the context of normothermic machine perfusion

Normothermic machine perfusion (NMP) is a technique that utilizes extracorporeal membrane oxygenation to recondition and repair kidneys at near body temperature prior to transplantation. The application of this new technology has been fueled by a significant increase in the use of the kidneys that were donated after cardiac death, which are more susceptible to ischemic injury. Preliminary results indicate that NMP itself may be able to repair marginal organs prior to transplantation. In addition, NMP serves as a platform for delivery of therapeutics. The isolated setting of NMP obviates problems of targeting a particular therapy to an intended organ and has the potential to reduce the harmful effects of systemic drug delivery. There are a number of emerging therapies that have shown promise in this platform. Nutrients, therapeutic gases, mesenchymal stromal cells, gene therapies, and nanoparticles, a newly explored modality, have been successfully delivered during NMP. These technologies may be effective at blocking multiple mechanisms of ischemia- reperfusion injury (IRI) and improving renal transplant outcomes. This review addresses the mechanisms of renal IRI, examines the potential for NMP as a platform for pretransplant allograft modulation, and discusses the introduction of various therapies in this setting.

Renoprotective Effects of Carbon Monoxide-Releasing Molecule 3 in Ischemia-Reperfusion Injury and Cisplatin-Induced Toxicity

BACKGROUND

We investigated the effects of a soluble carbon monoxide-releasing molecule (CORM) in cisplatin-induced cytotoxicity and ischemia-reperfusion injury (IRI) in vitro.

METHODS

The effects of CORM-3 (12.5-200 μM) were assessed in normal kidney epithelial cells (HK-2, LLC-PK1) and renal cancer cells (Caki-1, Caki-2) subjected to cisplatin (50-200 μM) or IRI. To induce IRI, cells were placed in an anaerobic chamber (37°C, 95% nitrogen, 5% carbon dioxide) for 48 hours. Cells were transferred to complete medium and incubated at 37°C, 5% carbon dioxide for 6 hours. Cell viability (CCK assays), tumor necrosis factor (TNF)-α messenger RNA (mRNA) levels (quantitative reverse-transcriptase polymerase chain reaction), and protein expression of cleaved-caspase 3 and oxidative stress markers (including Erk1/2, JNK, and P38; Western blot) were assessed.

RESULTS

Viability after IRI was approximately 40% of control. Protective effects of CORM-3 in the IRI model were dose-dependent. Cell viability was 40% recovered in 200-μM CORM-3-pretreated cells compared with control. The protective effects of CORM-3 in cells exposed to cisplatin for 24 hours were weaker than in the IRI model. TNF-α mRNA was induced by stimulated IRI or cisplatin exposure; CORM-3 pretreatment attenuated the rise in TNF-α mRNA. IRI or cisplatin-induced activated oxidative stress markers decreased in CORM-3-pretreated cells. CORM-3 reduced expression of the apoptotic marker cleaved-caspase 3.

CONCLUSION

Our data demonstrate the protective effects of CORM-3 in cisplatin cytotoxicity and IRI in both normal kidney cells and renal cancer cells in vitro. CORM-3 exerts these effects by ameliorating inflammatory and oxidative stress pathways.

Carbon Monoxide and Its Controlled Release: Therapeutic Application, Detection, and Development of Carbon Monoxide Releasing Molecules (CORMs)

Carbon monoxide (CO) is attracting increasing attention because of its role as a gasotransmitter with cytoprotective and homeostatic properties. Carbon monoxide releasing molecules (CORMs) are spatially and temporally controlled CO releasers that exhibit superior and more effective pharmaceutical traits than gaseous CO because of their chemistry and structure. Experimental and preclinical research in animal models has shown the therapeutic potential of inhaled CO and CORMs, and the biological effects of CO and CORMs have also been observed in preclinical trials via the genetic modulation of heme oxygenase-1 (HO-1). In this review, we describe the pharmaceutical use of CO and CORMs, methods of detecting CO release, and developments in CORM design and synthesis. Many valuable clinical CORMs formulated using macromolecules and nanomaterials are also described.

Norborn-2-en-7-ones as physiologically-triggered carbon monoxide-releasing prodrugs

A prodrug strategy for the release of the gasotransmitter carbon monoxide (CO) at physiological pH, based upon 3a-bromo-norborn-2-en-7-one Diels–Alder cycloadducts has been developed.

A prodrug strategy for the release of the gasotransmitter CO at physiological pH, based upon 3a-bromo-norborn-2-en-7-one Diels–Alder cycloadducts of 2-bromomaleimides and 2,5-dimethyl-3,4-diphenylcyclopentadienone has been developed. Examples possessing protonated amine and diamine groups showed good water solubility and thermal stability. Half-lives for CO-release in TRIS-sucrose buffer at pH 7.4 ranged from 19 to 75 min at 37 °C and 31 to 32 h at 4 °C. Bioavailability in rats was demonstrated by oral gavage and oCOm-21 showed a dose dependent vasorelaxant effect in pre-contracted rat aortic rings with an EC₅₀ of 1.6 ± 0.9 μM. Increased intracellular CO levels following oCOm-21 exposure were confirmed using a CO specific fluorescent probe.

Polymer–protein hybrid scaffolds as carriers for CORM-3: platforms for the delivery of carbon monoxide (CO)

The carbon monoxide releasing molecule, CORM-3, was grafted onto a polymer–protein conjugate thereby improving its half-life and release characteristics.

Controlled therapeutic gas delivery systems for quality-improved transplants

Therapeutic gases enriched into perfusion solutions have been effectively used for the improvement of organ transplant quality. At present, the enrichment of perfusion solutions with gases requires complex machinery/containers and handling precautions. Alternatively, the gas is generated within the perfusion solution by supplemented carbonylated transition metal complexes with associated toxicological concerns when these metals contact the transplant. Therefore, we developed therapeutic gas releasing systems (TGRSs) allowing for the controlled generation and release of therapeutic gases (carbon monoxide and hydrogen sulfide) from otherwise hermetically sealed containers, such that the perfusion solution for the transplant is saturated with the gas but no other components from the TGRS are liberated in the solution. The release from the TGRS into the perfusion solution can be tailored as a function of the number and thickness of gas permeable membranes leading to release patterns having been linked to therapeutic success in previous trials. Furthermore, the surrogate biomarker HMGB1 was significantly downregulated in ischemic rat liver transplants perfused with enriched CO solution as compared to control. In conclusion, the TGRS allows for easy, reliable, and controlled generation and release of therapeutic gases while removing safety concerns of current approaches, thereby positively impacting the risk benefit profile of using therapeutic gases for transplant quality improvement in the future.

Determination of the Preferred Conditions for the Isolated Perfusion of Porcine Kidneys

Background: The isolated perfused porcine kidney (IPPK) model has been the method of choice for the early preclinical evaluation of kidney graft preservation techniques. The preferred reperfusion conditions have not yet been determined. Here, we examined the effects of pressure- or flow-controlled perfusion and oxygenation by pure oxygen or carbogen (95% O2/5% CO2) on normothermic reperfusion in the IPPK model. Methods: Porcine kidneys were cold-stored for 24 h in histidine-tryptophan-ketoglutarate solution and reperfused for 1 h with normothermic whole blood/Krebs-Henseleit buffer medium (20/80%). Kidneys (n = 5/group) were flow-controlled reperfused with pure oxygen (1 ml/min/g; Flow-O2) or pressure-controlled reperfused (85 mm Hg mean arterial pressure) and oxygenated with either pure oxygen (Pressure-O2) or carbogen (Pressure-O2/CO2). Renal function and damage were assessed during reperfusion and NGAL and HIF-1α levels were analyzed using an ELISA. Results: Pressure-O2 and Pressure-O2/CO2 were associated with significantly better renal hemodynamics and acid-base homeostasis compared to Flow-O2. Urine protein concentrations and the fractional excretion of sodium were lower with both Pressure-O2 and Pressure-O2/CO2 than with Flow-O2. NGAL and HIF-1α levels were also lower with Pressure-O2 and Pressure-O2/CO2 than with Flow-O2. Only Pressure-O2/CO2 could demonstrate a significantly increased urine production compared to Flow-O2. The structural integrity was well preserved in the Pressure-O2 and Pressure-O2/CO2 groups, whereas diffuse and global glomerular destruction was observed in the Flow-O2 group. Conclusion: In the IPPK model, the application of pressure-controlled reperfusion with carbogen oxygenation, and to a lesser extent with pure oxygen, maintained physiological renal function for 1 h, thus providing a reliable and reproducible ex vivo evaluation of kidney preservation quality.

Anti-inflammatory effects of carbon monoxide-releasing molecule on trinitrobenzene sulfonic acid-induced colitis in mice

BACKGROUND AND AIM

Recent findings indicate that carbon monoxide (CO) in non-toxic doses exerts a beneficial anti-inflammatory action in various experimental models. However, the precise anti-inflammatory mechanism of CO in the intestine remains unclear. Here, we assessed the effects of a novel water-soluble CO-releasing molecule, CORM-3, on trinitrobenzene sulfonic acid (TNBS)-induced colitis in mice.

METHODS

To induce colitis, C57BL/6 male mice received an enema of TNBS. CORM-3 or its inactive compound, iCORM-3, were administered intraperitoneally, once immediately before, and twice daily after receiving an enema of TNBS. Three days after TNBS administration, the distal colon was removed, assessed for colonic damage and histological scores, polymorphonuclear leukocyte recruitment (tissue-associated myeloperoxidase, MPO activity), and TNF-α, IFN-γ and IL-17A expression (mRNA and protein levels in the colon mucosa). CD4(+) T cells isolated from murine spleens were stimulated with anti-CD3/CD28, in the presence or absence of CORM-3/iCORM-3. The cell supernatants were assessed for TNF-α and IFN-γ expression, 24 h following stimulation.

RESULTS

Colonic damage and histological scores were significantly increased in TNBS-induced mice compared to sham-operated mice. Tissue-associated MPO activity and expression of TNF-α, IFN-γ, and IL-17A in the colonic mucosa were higher in TNBS-induced colitis mice. The above changes were attenuated in CORM-3-treated mice. Further, CORM-3 was effective in reducing TNF-α and IFN-γ production in anti-CD3/CD28-stimulated CD4(+) T cells.

CONCLUSIONS

These findings indicate that CO released from CORM-3 ameliorates inflammatory responses in the colon of TNBS-challenged mice at least in part through a mechanism that involves the suppression of inflammatory cell recruitment/activation.

Heme oxygenase-1 as a target for drug discovery

SIGNIFICANCE

Heme oxygenase enzymes, which exist as constitutive (HO-2) and inducible (HO-1) isoforms, degrade heme to carbon monoxide (CO) and the bile pigment biliverdin. In the last two decades, substantial scientific evidence has been collected on the function of HO-1 in cell homeostasis, emphasizing these two important features: (i) HO-1 is a fundamental "sensor" of cellular stress and directly contributes toward limiting or preventing tissue damage; (ii) the products of HO-1 activity dynamically participate in cellular adaptation to stress and are inherently involved in the mechanisms of defence.

RECENT ADVANCES

On the basis of its promising cytoprotective features, scientists have pursued the targeting of HO-1 as an attractive cellular pathway for drug discovery. Three different pharmacological approaches are currently being investigated in relation to HO-1, namely the use of CO gas, the development of CO-releasing molecules (CO-RMs), and small molecules possessing the ability to up-regulate HO-1 in cells and tissues. CRITICAL ISSUE: Studies on the regulation and amplification of the HO-1/CO pathway by selective pharmacological approaches may lead to the discovery of novel drugs for the treatment of a variety of diseases.

FUTURE DIRECTIONS

In this review, we will discuss in detail the importance of pharmacologically manipulating the HO-1 pathway and its products for conferring protection against a variety of conditions that are characterized by oxidative stress and inflammation. We will also evaluate each of the strategic approaches being developed by considering their intrinsic advantages and disadvantages, which may have implications for their use as therapeutics in specific pathological conditions.

Emerging role of gasotransmitters in renal transplantation

Once patients with kidney disease progress to end-stage renal failure, transplantation is the preferred option of treatment resulting in improved quality of life and reduced mortality compared to dialysis. Although 1-year survival has improved considerably, graft and patient survival in the long term have not been concurrent, and therefore new tools to improve long-term graft and patient survival are warranted. Over the past decades, the gasotransmitters nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) have emerged as potent cytoprotective mediators in various diseases. All three gasotransmitters are endogenously produced messenger molecules that possess vasodilatory, anti-apoptotic, anti-inflammatory and anti-oxidant properties by influencing an array of intracellular signaling processes. Although many regulatory functions of gasotransmitters have overlapping actions, differences have also been reported. In addition, crosstalk between NO, CO and H2S results in synergistic regulatory effects. Endogenous and exogenous manipulation of gasotransmitter levels modulates several processes involved in renal transplantation. This review focuses on mechanisms of gas-mediated cytoprotection and complex interactions between gasotransmitters in renal transplantation.

Role of carbon monoxide in kidney function: is a little carbon monoxide good for the kidney?

Carbon monoxide (CO) is an endogenously produced gas resulting from the degradation of heme by heme oxygense or from fatty acid oxidation. Heme oxygenase (HO) enzymes are constitutively expressed in the kidney (HO-2) and HO-1 is induced in the kidney in response to several physiological and pathological stimuli. While the beneficial actions of HO in the kidney have been recognized for some time, the important role of CO in mediating these effects has not been fully examined. Recent studies using CO inhalation therapy and carbon monoxide releasing molecules (CORMs) have demonstrated that increases in CO alone can be beneficial to the kidney in several forms of acute renal injury by limiting oxidative injury, decreasing cell apoptosis, and promoting cell survival pathways. Renal CO is also emerging as a major regulator of renal vascular and tubular function acting to protect the renal vasculature against excessive vasoconstriction and to promote natriuresis by limiting sodium reabsorption in tubule cells. Within this review, recent studies on the physiological actions of CO in the kidney will be explored as well as the potential therapeutic avenues that are being developed targeting CO in the kidney which may be beneficial in diseases such as acute renal failure and hypertension.

Carbon monoxide: an unusual drug

The highly toxic gas carbon monoxide (CO) displays many physiological roles in several organs and tissues. Although many diseases, including cancer, hematological diseases, hypertension, heart failure, inflammation, sepsis, neurodegeneration, and sleep disorders, have been linked to abnormal endogenous CO metabolism and functions, CO administration has therapeutic potential in inflammation, sepsis, lung injury, cardiovascular diseases, transplantation, and cancer. Here, insights into the CO-based therapy, characterized by the induction or gene transfer of heme oxygenase-1 and either gas or CO-releasing molecule administration, are reviewed.

Use of carbon monoxide in minimizing ischemia/reperfusion injury in transplantation

Although carbon monoxide (CO) is known to be toxic because of its ability to interfere with oxygen delivery at high concentrations, mammalian cells endogenously generate CO primarily via the catalysis of heme by heme oxygenases. Recent findings have indicated that heme oxygenases and generation of CO serve as a key mechanism to maintain the integrity of the physiological function of organs and supported the development of a new paradigm that CO, at low concentrations, functions as a signaling molecule in the body and exerts significant cytoprotection. Consequently, exogenously delivered CO has been shown to mediate potent protection in various injury models through its anti-inflammatory, vasodilating, and antiapoptotic functions. Ischemia/reperfusion (I/R) injury associated with organ transplantation is one of the major deleterious factors limiting the success of transplantation. Ischemia/reperfusion injury is a complex cascade of interconnected events involving cell damage, apoptosis, vigorous inflammatory responses, microcirculation disturbance, and thrombogenesis. Carbon monoxide has a great potential in minimizing I/R injury. This review will provide an overview of the basic physiology of CO, preclinical studies examining efficacy of CO in I/R injury models, and possible protective mechanisms. Carbon monoxide could be developed to be a valuable therapeutic molecule in minimizing I/R injury in transplantation.

No synergistic effect of carbon monoxide and oxygen during static gaseous persufflation preservation of DCD livers

OBJECTIVE

The benefit of carbon monoxide and/or oxygen as applied by controlled, continuous gaseous persufflation during liver preservation on postischemic graft recovery was investigated in an isolated rat liver model.

METHODS

Livers from male Wistar rats were retrieved 30 min after cardiac arrest of the donor and subjected to 18 h of cold storage. Some grafts were subjected to gaseous persufflation during static cold storage either with pure oxygen or with CO dissolved in oxygen. Graft integrity was assessed thereafter upon warm reperfusion in vitro.

RESULTS

Oxygen persufflation significantly reduced cellular enzyme loss and metabolic recovery (bile production and ATP recovery) upon reperfusion by about 50%. The effect was associated with a reduction of vascular perfusion resistance, mitigated gene up-regulation of the mitochondrial stress protein GRP 75, and improved mitochondrial ultra-structure. Similar results were obtained by persufflation with CO in oxygen, while no additive benefit of CO and oxygen could be seen in our model.

CONCLUSION

Hepatocellular injury of cold stored liver grafts can be notably reduced by gaseous ex vivo application of oxygen with or without additional admixture of CO to the isolated organ but no superiority or additive effect is seen with respect to persufflation with oxygen.

Inhaled carbon monoxide prevents acute kidney injury in pigs after cardiopulmonary bypass by inducing a heat shock response

BACKGROUND

Cardiopulmonary bypass (CPB) may be associated with acute kidney injury (AKI). Inhaled carbon monoxide (CO) is cyto- and organ-protective. We hypothesized that pretreatment with inhaled CO prevents CPB-associated AKI.

METHODS

Pigs (n = 38) were nonrandomly assigned to SHAM, standard CPB, pretreatment with inhaled CO (250 ppm, 1 hour) before SHAM or CPB, to pretreatment with quercetin (an inhibitor of the heat shock response), and to pretreatment with SnPPIX (an inhibitor of endogenously derived CO), before CO inhalation and CPB. The primary outcome variables were markers of AKI (urea, uric acid, creatinine, cystatin C, neutrophil gelatinase-associated lipocalin, interleukin-6, tumor necrosis factor-alpha), which were determined 120 minutes after CPB. Secondary outcome variables were heat shock protein (HSP)-70 and heme oxygenase-1 protein expressions as indicators of CO-mediated heat shock response.

RESULTS

Pretreatment with inhaled CO attenuated (all P < 0.001) CPB-associated, (1) increases in serum concentrations of cystatin C (64 +/- 14 vs 28 +/- 9 ng/mL), neutrophil gelatinase-associated lipocalin (391 +/- 65 vs 183 +/- 56 ng/mL), renal tumor necrosis factor-alpha (450 +/- 73 vs 179 +/- 110 pg/mL), and interleukin-6 (483 +/- 102 vs 125 +/- 67 pg/mL); (2) increase in renal caspase-3 activity (550 +/- 66 vs 259 +/- 52 relative fluorescent units); and (3) histological evidence of AKI. These effects were accompanied by activation of HSP-70 (196 +/- 64 vs 554 +/- 149 ng/mL, P < 0.001). Pretreatment with the heat shock response inhibitor quercetin counteracted the CO-associated biochemical and histological renoprotective effects (all P < 0.001), whereas the heme oxygenase inhibitor SnPPIX only partially counteracted the CO-associated renoprotection and the activation of the heat shock response.

CONCLUSIONS

CO treatment before CPB was associated with evidence of renoprotection, demonstrated by fewer histological injuries and decreased cystatin C concentrations. The findings that the antiinflammatory and antiapoptotic effects of CO were accompanied by activation of HSP-70, which in turn were reversed by quercetin, suggest that renoprotection by pretreatment with inhaled CO before CPB is mediated by activation of the renal heat shock response.

Gaseous persufflation with carbon monoxide during ischemia protects the isolated liver and enhances energetic recovery

BACKGROUND

The benefit of carbon monoxide as applied by controlled, continuous gaseous persufflation during liver preservation on postischemic graft recovery was investigated in an isolated rat liver model.

METHODS

Livers from male Wistar rats were retrieved 30 min after cardiac arrest of the donor and subjected to 18 h of cold storage. Some grafts were subjected to gaseous persufflation with carbon monoxide (CO, dissolved in nitrogen) during static cold storage at a concentration of 50 ppm or 250 ppm. Graft viability was assessed thereafter upon warm reperfusion in vitro.

RESULTS

CO-persufflation significantly reduced cellular enzyme loss (maximal at 50 ppm) and functional recovery (bile production and energy charge) upon reperfusion by about 50%. The effect was associated with a reduction of free radical-induced lipid peroxidation, lower vascular perfusion resistance, and improved mitochondrial ultrastructure.

CONCLUSION

Viability of cold stored liver grafts can be notably augmented by gaseous ex vivo application of low dose CO to the isolated organ.

Ex vivo application of carbon monoxide in UW solution prevents transplant-induced renal ischemia/reperfusion injury in pigs

I/R injury is a major deleterious factor of successful kidney transplantation (KTx). Carbon monoxide (CO) is an endogenous gaseous regulatory molecule, and exogenously delivered CO in low concentrations provides potent cytoprotection. This study evaluated efficacies of CO exposure to excised kidney grafts to inhibit I/R injury in the pig KTx model. Porcine kidneys were stored for 48 h in control UW or UW supplemented with CO (CO-UW) and autotransplanted in a 14-day follow-up study. In the control UW group, animal survival was 80% (4/5) with peak serum creatinine levels of 12.0 +/- 5.1 mg/dL. CO-UW showed potent protection, and peak creatinine levels were reduced to 6.9 +/- 1.4 mg/dL with 100% (5/5) survival without any noticeable adverse event or abnormal COHb value. Control grafts at 14 days showed significant tubular damages, focal fibrotic changes and numerous infiltrates. The CO-UW group showed significantly less severe histopathological changes with less TGF-beta and p-Smad3 expression. Grafts in CO-UW also showed significantly lower early mRNA levels for proinflammatory cytokines and less lipid peroxidation. CO in UW provides significant protection against renal I/R injury in the porcine KTx model. Ex vivo exposure of kidney grafts to CO during cold storage may therefore be a safe strategy to reduce I/R injury.

Simulated urban carbon monoxide air pollution exacerbates rat heart ischemia-reperfusion injury

Myocardial damages due to ischemia-reperfusion (I/R) are recognized to be the result of a complex interplay between genetic and environmental factors. Epidemiological studies suggested that, among environmental factors, carbon monoxide (CO) urban pollution can be linked to cardiac diseases and mortality. The aim of this work was to evaluate the impact of exposure to CO pollution on cardiac sensitivity to I/R. Regional myocardial I/R was performed on isolated perfused hearts from rats exposed for 4 wk to air enriched with CO (30-100 ppm). Functional variables, reperfusion ventricular arrhythmias (VA) and cellular damages (infarct size, lactate dehydrogenase release) were assessed. Sarcomere length shortening and Ca(2+) handling were evaluated in intact isolated cardiomyocytes during a cellular anoxia-reoxygenation protocol. The major results show that prolonged CO exposure worsens myocardial I/R injuries, resulting in increased severity of postischemic VA, impaired recovery of myocardial function, and increased infarct size (60 +/- 5 vs. 33 +/- 2% of ischemic zone). The aggravating effects of CO exposure on I/R could be explained by a reduced myocardial enzymatic antioxidant status (superoxide dismutase -45%; glutathione peroxidase -49%) associated with impaired intracellular Ca(2+) handling. In conclusion, our results are consistent with the idea that chronic CO pollution dramatically increases the severity of myocardial I/R injuries.

Carbon monoxide: endogenous mediator, potential diagnostic and therapeutic target

The primary objectives of this article are to review the potential role of carbon monoxide (CO) as an endogenous mediator, diagnostic marker for pulmonary disorders, and therapeutic target in critical illness. The review will start by focusing on the importance of the heme oxygenase (HO)-CO axis as an endogenous system as it relates to the cardiovascular and pulmonary systems. It will elucidate the influence of HO gene expression on critical events like shock, sepsis, ischemia-reperfusion and others. Our focus will then shift and look at the potential diagnostic role of exhaled CO in major inflammatory states of the lung, and finally we will highlight the activities on inhaled CO being considered as a possible therapeutic tool and the controversies surrounding it.

Carbon monoxide reduces pulmonary ischemia-reperfusion injury in miniature swine

OBJECTIVES

Carbon monoxide is produced endogenously as a by-product of heme catalysis and has been shown to reduce ischemia-reperfusion injury in a variety of organs in murine models. The aims of this translational research were to establish an in situ porcine lung model of warm ischemia-reperfusion injury and to evaluate the cytoprotective effects of low-dose inhaled carbon monoxide in this model.

METHODS

Warm ischemia was induced for 90 minutes by clamping the left pulmonary artery and veins in 8 Clawn miniature swine (Japan Farm CLAWN Institute, Kagoshima, Japan). The left main bronchus was also dissected and reanastomosed just before reperfusion. Four animals were treated with inhaled carbon monoxide at a concentration of approximately 250 ppm throughout the procedure. Lung function and structure were serially accessed via lung biopsy, chest x-ray films, and blood gas analysis.

RESULTS

Carbon monoxide inhalation dramatically decreased the lung injury associated with ischemia and reperfusion. Two hours after reperfusion, the arterial oxygen tension of the carbon monoxide-treated group was 454 +/- 34 mm Hg, almost double the arterial oxygen tension of the control group (227 +/- 57 mm Hg). There were fewer pathologic changes seen on chest x-ray films and in biopsy samples from animals in the carbon monoxide-treated group. Animals in the carbon monoxide-treated group also had fewer inflammatory cell infiltrates and a markedly smaller increase in serum concentrations of the proinflammatory cytokines interleukin 1beta, interleukin 6, and high-mobility group box 1 after ischemia-reperfusion injury.

CONCLUSIONS

The perioperative administration of low-dose inhaled carbon monoxide decreases warm ischemia-reperfusion injury in lungs in miniature swine. This protective effect is mediated in part by the downregulation of proinflammatory mediators.